Bacteria in wastewater harnessed for electricity

Portland, Ore.  An environmental engineer has found a way not only to cleanse contaminated wastewater with its own bacteria but to generate electricity from the funky flow.

Lars Angenent, an assistant professor of chemical engineering at Washington University (St. Louis), has already prototyped his findings in a device the size of a thermos bottle  a variation on the hydrogen fuel cell  but he knows it will have to scale up dramatically to fill a commercial role.

With scaled-up capacity, Angenent said, a large food-processing plant, which now must cleanse its water at a cost, would be able to turn that processing into a profit center. Industrial-scale wastewater treatment plants, he said, could produce enough electricity to power thousands of households while simultaneously cleansing their water.

Angenent's microbial fuel cell design uses the bacteria from wastewater on its anode and cathode instead of platinum, enabling it to make a fuel from the water to create electricity while simultaneously neutralizing the biological matter that would otherwise have to be purged from the water.

In the typical hydrogen fuel cell, a membrane separates the device's anode and cathode into two side-by-side chambers. Hydrogen fuel reaching the anode electrode splits into protons, which migrate across the membrane through the liquid medium, and electrons, which travel over a wire to the cathode, thereby generating electricity. Meanwhile, oxygen in the cathode chamber combines with the protons to form water. A heavy metal like platinum is required to plate the anode to catalyze the reaction.

By contrast, Angenent's microbial fuel cell uses a carbon-based foam with large pores in which the bacteria from the wastewater are promoted to grow. The bacteria then catalyze the reaction, enabling electricity to flow from the anode to the cathode using nothing more than the biological agents in the wastewater as fuel. "In a microbial fuel cell, the organic material in the water will be the fuel and instead of platinum. . . you use microbial cells [bacteria] to do the catalysis," said Angenent.

Bacteria oxidize the organic material in wastewater to produce the electrons and protons, with the electrons traveling from the anode to the cathode through a conductive wire and the protons moving by diffusion through the solution and the membrane separating the anode and the cathode chambers.

"Today, contaminated water is treated in giant reactors that produce methane and carbon dioxide gas," Angenent said. "But the microbial fuel cell would use these treatment chambers to produce electricity instead."

Angenent estimated that a bioelectricity-generating wastewater treatment system based on a scaled-up version of the microbial fuel cell has the potential to power about 900 single-family American households from a single food-processing plant. Angenent performed the research in consultation with professor Shelley Minteer at St. Louis University and with the assistance of Washington University doctoral candidate Jason He.

Angenent's team continues to optimize the reactor configuration, with their next step being optimization of the reactor's operation and, finally, building a large system capable of processing millions of gallons of wastewater. "We believe that larger versions will be able to be used for local-neighborhood electricity generation," he said. "I want to have a large pilot-scale system within 10 years."

Angenent has applied for a patent on the stacked microbial fuel cell design and received preliminary funding from Washington University to scale up the device. The university hopes to license it commercially to existing companies or to fund its own startup.

Biofuel cells have been scientifically validated since the 1950s, but were mainly researched for medical purposes.